Amyloidosis. Light micrograph of amyloid nodules (blue) in a human spleen. The intervening purple- staining area is normal spleen tissue. Amyloidosis is an uncommon disease in which deposits of a fibrous protein called amyloid accumulate in body tissues for no known reason. The condition is sometimes associated with other diseases, such as rheumatoid arthritis, bone marrow cancer and tuberculosis. Progressive deposition of the protein damages the function of the affected organ. Amyloidosis of the heart can lead to heart failure, for instance, while amyloidosis of the kidney can cause renal failure. Treatment is of the underlying condition, if one is known. Magnification x20 at 6x9cm size.